1. Field of the Invention
This invention relates to transition metal complexes with ancillary ligands, and in particular, to acyclic anionic six-electron donor ancillary ligands.
2. Background Art
The chemical industry uses a wide variety of transition metal complexes as catalysts for organic reactions. Olefin polymerization is an important example of such a reaction. While conventional Ziegler-Natta catalysts continue to dominate the industry, highly active metallocene or single-site catalysts which provide polymers with properties such as narrow molecular weight distributions, low densities, and good co-monomer incorporation, are emerging.
Transition metal complexes used to polymerize olefins are normally non-zero-valent metals (e.g., Ti4+, Zr4+, Sc3+) surrounded by anionic ligands (e.g., chloride, alkyl, cyclopentadienyl) that satisfy the valency of the metal. The nature of the various anionic ligands can dramatically affect catalyst activity and polymer properties. Thus, by varying the choice of anionic ligand, a catalyst structure can be fine-tuned to produce polymers with desirable properties. Furthermore, the anionic ligand will affect the stability of the transition metal complexes.
Metallocene polymerization catalysts contain one or two cyclopentadienyl groups as anionic ligands. These serve to stabilize the active catalytic species, modulate the electronic and steric environment around the active metal center, and maintain the single-site nature of the catalyst. Polymers with narrow molecular weight and composition distributions may be produced using these metallocene catalysts. Such complexes frequently contain substituted cyclopentadienyl groups. By utilizing substituted cyclopentadienyl moieties, the geometry and electronic character of the active site may be altered, thus altering the activity and stability of the catalyst as well as the properties of the polyolefins produced therefrom.
Further anionic ligands are those which are heteroatomic ring ligands isolobal to the cyclopentadienyl ring; that is, the orbital interaction of the metal with the ligand is similar in both cases. Examples of such ligands are boraaryl (see, e.g., U.S. Pat. No. 5,554,775), pyrrolyl and indolyl anions (U.S. Pat. No. 5,539,124), azaborolinyl groups (U.S. Pat. No. 5,902,866), phospholyl anions, and tris(pyrazolyl)borate anions.
Transition metal complexes with highly delocalized cyclic anionic six-electron-donor ancillary ligands are important precursors for a variety of highly efficient catalysts. The performance and cost of these catalysts are strongly dependent on the structure of the ligands. It would be desirable to provide transition metal complex catalysts in addition to those presently available in order to provide further options with regard to catalytic activity and stability and polyolefin product properties.
In one embodiment of the present invention, a delocalized anionic acyclic ligand capable of providing six electrons when coordinated to a transition metal is provided. The structure of the ligand of the present invention is given by: 
where A is CH2, CHR3, CR3R4, NR3, O, S, or PR3; R1 and R2 are each independently hydrogen, an aryl group, preferably a C6-15 aryl group, a C6-15 arylphospho group (each aryl is C6-5), a C6-15 arylthio group, C7-15 aralkyl group, C1-10 alkoxy group, C6-14 aryloxy group, a C1-10 dialkylamino group (each alkyl is C1-10), or a C6-15 diarylamino group (each aryl is C6-15); R3 and R4 are each independently hydrogen, a C1-8 alkyl group, C6-10 aryl group, or C7-15 aralkyl group; and Y is B, Al, or Ga. It should be noted that in compounds containing xe2x80x9cC6-15 diarylxe2x80x9d groups and similar designations, the C6-15 refers to each aryl group rather than the total carbon content of the ligand.
In another embodiment of the present invention, a transition metal complex incorporating the ligand of structure I is provided. The structure of the complex of the present invention is: 
where M is a transition metal; L is a sigma bonded or pi bonded ligand; n is an integer such that the valency of M is satisfied; A is CH2, CHR3, CR3R4, NR3, O, S, and PR3; R1 and R2 are each independently hydrogen, C6-10 aryl, diarylphospho, C1-8 alkylthio, C6-15 arylthio, C7-15 aralkyl, C1-10 alkoxy group, C6-14 aryloxy group, C1-10 dialkylamino group, or C6-15 diarylamino group; R3 and R4 are each independently hydrogen, C1-8 alkyl, C6-10 aryl, C7-15 aralkyl, C1-10 alkoxy, C6-14 aryloxy, C1-10 dialkylamino, or C6-15 diarylamino, and Y is B, Al, or Ga.
In still another embodiment of the present invention, a method for forming the metal complex having the ligand of the present invention is provided. The method comprises reacting a ligand precursor having the following structure: 
where Z is a leaving group, with a metal compound with the structure:
Xxe2x80x94Mxe2x80x94Lnxe2x80x83xe2x80x83IV
where X is a halogen, to form metal complex II. L and n are as defined above.